The present invention relates to a liquid developer for developing electrostatic images formed by electrophotography or electrostatography such as electrostatic recording, etc.
Liquid developers for electrostatic images are generally composed of a nonaqueous medium having a high electrical resistance and a low dielectric constant such as aliphatic hydrocarbons or toluene, etc. and particles of various kinds of coloring agents such as carbon black or phthalocyanine, etc. dispersed therein. Generally, a resin is allowed to adhere to the surface of particles of the coloring agent in order to control electrostatic charges and bestow dispersibility or fixability, etc. so that the coloring agent can be used as a toner. Further, if necessary, additives such as a dispering agent or a polarity controller, etc. are added to the nonaqueous medium.
Examples of known resins which adhere to the coloring agent include natural resins and synthetic resins such as rosin, natural rubber, alkyd resin, phenol resin, epoxy resin, pentaerythritol resin, acryl resin and synthetic rubber. However, there are practical problems with using these resins. For example, it is difficult to obtain the natural resins in constant quality and the synthetic resins such as acryl resin are not desirable because sufficient dispersibility and fixability can not always be obtained and aggregation or precipitation of particles is easily caused by the passage of time.
The present inventors have carried out earnest studies in order to improve the above described faults and have developed the present invention.